STREAMS Data

Data on a stream is passed in the form of messages. Messages are
the means by which all I/O is done under STREAMS. Each stream head, STREAMS
module, and driver has a read sideand a write
side. When messages go from one module's read side to the next
module's read side, they are said to be traveling upstream. Messages passing
from one module's write side to the next module's write side are said to be
traveling downstream. Kernel-level operation of messages is discussed in Message Components.